Method of recovering hydrocarbons



Oct 7, 1942- H. R. LEGATSKI ET AL METHOD OF RECOVERING' HYDROCARBONS Filed Dec. 21, 1957 3 Sheets-Sheet 2 1942- H. R. LEGATSKI ET AL METHOD OF RECOVERING HYDROCARBONS Filed Dec. 21, 1937 3 Sheets-Sheet 5 NEYS.

W O PU FDO Patented Oct. 27, 1942 2.29am METHOD oraacovsamc maocannoss naroidLLegatskLWillSwa-dlomandGerfld W.l\loall oagh. Bartleoville, Okla-,ansignorsto cumin m, I mm 0 were I Application December 21,1931, serum. mas:

8 Claims. (Cl- 196-4) This invention relates to an improved method for recovering all but the most volatile fraction of hydrocarbon gases.

An important object of the invention is recover a greater amount of the desirable fractions without increasing the distillation equipment.

A further important object of the invention is to recover a larser amount 01' the lighter or more volatile desirable fractions without unduly increasing the recovery of the more volatile undesirable fractions.

A still further object of the invention is to effect a rough separation of the absorbed components according to volatility.

Referring to the drawings,

Fig. 1 is a diagrammatic view 01' a system embodying the present invention,

Fig. 2 is a diagrammatic view of a system embodying a modification, and

Fig. 3 is a diagrammatic view of a system embodying a further modification.

Referring to Fig. 1, a main absorber is shown at I I and supplemental absorbers at l2, I3 and I4. A gas admission pipe l5 enters the lower part of absorber II and a residue gas pipe I3. is arranged at its upper end having a back pressure regulator l1. Pipes l8, |9, 25', 32', and 33' are connected to absorber H for the admission of absorption oil, pipes I9, 25', 32' and 33' having branches for admitting the oil at various plates of the absorber. Connected to the lower end of absorber fl 'is a rich absorption oil pipe 23 con trolled by level control 2| and connected to a vent tank 22. The vapor space in vent tank 23 is connected by pipe 23 controlled by back pressure regulator 24 to the lower end of absorber l2. A pipe 25 for absorption oil, controlled by level controller 26, connects vent tank 22 with a second vent tank 21. The lower end of absorber I2 is also connected to vent tank 21 for absorption oil ilow through a pipe 2!! controlled by level control 29. The vapor space of vent tank 21 is connected by pipe 30, controlled by back pressure regulator 3|, with the lower end of absorber l3. A pipe 32 for absorption oil, controlled by level control 33, connects vent tank 21 with a third vent tank 34. A pipe 35 for absorption oil, controlled bylevel controller 38, also connects the lower end of absorber I3 with vent tank 34. The vapor space of vent tank 34 is connected with the lower end or absorber |4 through a pipe 31 controlled by back pressure regulator 33. A pipe 33 for absorption oil, controlled by level controller 43, connects vent tank 34 with a fourth vent tank 4|.

Absorber 4 is also connected with vent tank 4| connected with pipes'fl', 32' and 33' respectively.

The vapor space of vent tank 4| is connected with acompressor 44 through pipe 4! controlled by back pressure regulator 43. The discharge from compressor 44 by means of pipe 41 is connected to a storage tank 43, pipe 41 having a cooling section 43 in cooling tower 53. Connected to vent tank 4| is a pipe 5| for absorption'oll controlled by level control 52 having a branch 53 going to a conventional distillation unit 54 through a heater I4 and a branch 55 going through pump 53 to pipe l3. The overhead from distillation unit'54 can pass to cooling section 43 or any other condenser through pipe 51, the lean oil from the distillation unit passing to pipe l3. Pipe it has branches I 3' to conduct lean oil to the top of each of the absorbers l2, l3 and I4. These latter absorbers have residue gas pipes 58 having back pressure regulators 59. Heaters :0, 23', 35' and 42' are shown in pipes 23, 23, 35 and 42, and pipes I3, 25', 32'. and 33' pass through cooler IS. The

usual hand valves and. meters are shown in their desirable locations.

As shown in Fig. 1, a stream of partially denuded absorbent from pipe I! is introduced into absorber II at one or more appropriate points below the top plate. In order that no valuable constituents may be lost in the residue by stripping of the partially denuded absorbent, a stream of denuded absorbent from pipe I8 is introduced at the top plate to recover any stripped portion. Below the point of entry of partially denuded absorbent both liquid streams merge to give an effect of high absorbent rate in the bottom section of the absorber.

Heaters 23', 23', 35' and 42 may be used if desired either with or without pressure reduction. Pressure reduction and addition of heat are substantially' equivalent when venting a vapor of high methane content but where other vapors are present in solution the two methods have difierent results. Table I shows various methods of recovering vapors from a rich oil having a vapor pressure of 160 pounds at 70 F. v The various steps taken to secure substantially equivalent propane vaporization, shown in parentheses, do not yield equivalent amounts of other vaporized components.

Tsar: I

Rich oil Absolute premure 100! Temperature 70 Absolute pressure 751 75! Temperature 150 70 unn ed Me e 28. 07 42. 74 Ethane 65.71 85.00 Propane 84.03 05.46 Butanes 03. 28 08. 4.1 Pentancs W. 41 90. 62 Hermes $.92 90.83 Oil 100.00 100.00

1 l 4. Absolute pressure 15! 15! 35 'leltlyiperaturo 150 70 150 nva rized Met gne 1. 57 3. 81 6. 34 cm at :3) 63% Pro Butanes 63. 68- 98. 44 86. 67 Pentanes 83. 80 96. 42 94. 03 Hexanes 92. 42 W. 67 97. 83 11 100. 100. 00 100. 00 l l t t 1 Absolute pressure 3!. 3! 7. 8# 3! Ba! 'Iempentur 0 150 70 150 250 150 unva rlzed Met a 0. 03 0. 01 0. l3 0. 03 0. 21 Ethane 0. 95 4. 00 50. 4 0. 66 5. 05 Propane 6. 62 (22. 46) (22. 69) 3. 03 (22. 70) Butane: 21. 83 52. 12 48. 60 7. 86 47. 6 Pentones 50.00 U). 17 74. 07 17. 90 73. 71 Home! 71. 60 92. 00 87. 75 31. 08 87. 00 Oil 100. 00 100. 00 100. 00 100. 00 100. 00

In the present case the use of heater 20' is often not desirable from a technical viewpoint because in the vapors evolved less methane is present at higher temperatures and equivalent pressures than when using low temperatures and low pressure. In such instance the methane can be vented at low temperature and pressure in tank 22 and heat added before tanks 21, 34 and 4| for removal of the heavier fractions. As brought out by Table I distillation unit 54 can be omitted by designing the pressure and temperature differentials between the vent tanks so as to arrive at pressures of 2.5 to 3.5 pounds per square inch and temperatures of 250 to 300 F. in vent tank ll. These conditions will yield the same degree of denudation now used in gasoline plants for butane and heavier recovery. In such event pipe 53 would be closed.

To supplement the desired vaporization at any point in the applicant's system, the usual expedient of a stripping agent can be used. The liberation of dissolved gases and vapors is referred to in this specification as vaporization of such components or ebullition of the absorbent in which they are dissolved, whether it is caused by raising temperature, lowering pressure, or any other known expedient or any combination of them.

Rich absorbent leaves the bottom of absorber ll through pipe 20 and enters vent tank 22 operating at a pressure P: which is less than pressure P1 on absorber I I. Vapors evolved due to ebullition of the absorbent in tank 22 pass directly through pipe 23 to absorber l2 operating at pressure P: less pressure drop in regulator 24, where the heavier fractions are absorbed by a denuded absorbent stream entering at the top from pipe 18'. Rich absorbent from absorber l2 and flashed absorbent from vent tank 22 pass to vent tank 21 where pressure is again dropped to flash absorbed constituents. The same sequence of operations, namely, selectively flashing and reabsorbing occurs in vent tank 21 and absorber l3 and in vent tank 34 and absorber I4. It is obvious that this operation could continue as long as the pressure differential between succeeding vent tanks is great enough to induce sufllcient vaporization.

Rich absorbent, after successive flash vaporization and reabsorption of evolved vapors to retain low vapor pressure material, is finally flashed in vent tank 4| to pressure P5 which is as low as economically practical in order to induce a maximum vaporization of absorbed constituents. Vapors are recovered as liquid product by compression at 44 and subsequent cooling at 49.

Partially denuded absorbent from vent tank II is divided into two streams, one being pumped through pipe 55, pump 56, and pipe l9 directly back to absorber H and the other being sent through pipe 53 to a conventional distillation unit 54 for removal of all absorbed material. This distillate is shown as going directly to storage tank. 48 along with compression product although its composition may warrant special storage to facilitate later purification operations.

The absorption oil in vent tanks 22, 21 and I4 is denuded in increasing degree in the order named. If desired part of the oil from each vent may be recycled to absorber ll through pipes 25', 32 and 39', each such pipe having branches to respectively higher plates in the intermediate section of the absorber.

In Fig. 2 is shown a modification of the apparatus and method of Fig. 1. In this figure reference numeral 60 indicates an absorber having a gas inlet pipe 6| and a residue gas pipe 62 having a back pressure regulator 63. The pipe 84 is connected with absorber 60 at the top plate for the admission of absorption oil and a pipe 65 controlled by level control 66 is connected with the lower end of the absorber for the eduction of absorption oil to the lower end of combination vent tank and absorber 61. A pipe 68 having rate of flow control 69 admits lean oil to the top plate of the absorber section of tank 61. A residue gas pipe 10 having back pressure regulator 10', is connected to the top of tank 61. Absorption oil pipe 1| controlled by level control 12 connects the lower end of tank 61 with a vent tank 13, the upper end of vent tank 13 having a product pipe 14 controlled by back pressure regulator 15, which leads to a compressor 15, the discharge of which in turn is connected by a pipe 11 with condenser 18. The condensate and uncondensable products are conducted from condenser 18 through pipe 19 to product accumulator 80, the uncondensable products passing ofi through pipe 8| controlled by back pressure regulator 82. Absorption oil pipe 83 controlled by level control 84 is connected to the lower end of tank 13 which passes to a pump 85 driven by motor 85'. Output pipe 86 from pump 85 has a branch 86 leading to a second pump 81 driven by motor 85' which has output pipe 88 controlled by rate of flow controller 89.' Pipe 88 leads to a distillation unit 90 and has interposed in it belore unit I. a heater head hom distillation unit 00 passes to a condenser I. wherein steam till product is condemed. Tbemainlineotpipeelgoestoan intermediate plate of absorber II. A re-compressor product pipe II controlled by level con- The overtrol It connects with storage pipe 83. Steam still product pipe it connects with storage pipe ll. Pipes 80 and II are connected by a pipe 00 which in turn is connected with pipe 01 going to absorber 00 at a plate lower than that to which pipe I is connected.

- In tbeoperation oi the modification shown in I Fig. 2, partially denuded oil is introduced into a multi-plate absorber 00 at an intermediateoil's point of entrance. The rate of partially.

denuded oil fiow is greater than that of the lean oil. The applicants found that a ratio ofthree to one was satisfactory for the types or gases tested. The combined stream of oil then flows down the remainder or the column becoming saturated with the entering gas.

By recycling a portion or the recompressor or steam still product, or both. through pipe 01, into the first absorber at a point below the point of entry 0! the flash-vented oil, the combined liquid flowing down to the base oi the absorber becomes iurther saturated with the entering gas. The product to be recycled can be controlled as to molecular weight or vapor pressure by mixing the recompressor and steam still products.

Therich oil is then passed through a flashvent absorber 81 operating at a low pressure as a step !or removing the lightest fractions, in the present instance. methane. The flash-vent absorber is a combination vent tank and reabsorber unit 00 where it is denuded. The lean oil goes system is that it increases the amount of hydrocarbcns to berecovered from a gas by circulating more absorption oil or low molecular weight hydrocarbon liquid, and denuding the enriched oil without increasing steam still or heating requirements. Product is recovered from the additional amount of absorption oil by flashingthe rich oil in a vent tank operating under vacuum.. In other words, this absorption system substitutes compressors required ior producin: vacuum for heatdistillation units. Although only one flash-vent absorber is shown, several could be used. the number depending on the working pressure of the first absorber and the degree or demethanization desired.

Pig. 3,shows a further modification o! the apnects with absorber I00 at the top plate and. rich absorption oil pipe Ill controlled by level controller I00 connects the lower end or absorber I00 with the lower end oi. a combination vent tank and absorber I01. Combination vent tank and absorbers Ill and Ill, identical with I01, have their lower ends connected for absorption oil fiow through pipes IIO controlled by level controllers III. Part way up in the, absorber section of tanks I01, I00 and II! are located partitions III which permit gas to pass upwardly through them but prohibit the passage of oil downwardly. Pipes Ili controlled by back pressure regulators Ill connect the upper end of tanks I01 and I00 with the lower portion of the absorber section of tanks I00 and Ill respectively. Pipe III controlled by back pressure regulator Ill, connects the top of tank I00 with the residue gas line. A lean oil pipe III controlled by rate of flow controller I I6 is connected with a top plate of tank I00. 'Pipe II1 having pumps Ill connect the absorber section of tanks I09 and I00 above the partitions I I2 with the top plate oi the absorber sections of tanks I00 and I01 respectively. Absorption oil pipe H9 controlled by level control I20 connects the lower end of tank I09 with a vent tank I2I. Absorption oil pipe I 22 controlled by level control I23 is connected with the lower end of vent tank Ill and passes to a pump I20 driven by motor I25. A pipe I20 having a back pressure regulator I21 is connected to the upper end or vent tank I2I to conduct product to compressors. The output of pump I24 passes into pipe I28 which has a branch I29 controlled by rate of flow controller I 30 connecting with a conventional distilling unit. Pipe I20 enters absorber I00 at intermediate plate. Absorption oil pipe I BI is connected to the absorber section of tank I01 above and adjacent partition II! and joins with pipe I20.

In the operation of this modification flashvented oil is introduced into absorber I00 several plates below the top. At the top of theme absorber lean oil is added and flows down the column absorbing vapors rising from the point at which the flash-vented oil enters. At the point of entrance oi the partially denuded oil the two streams combine and flow down the remainder oi the column becoming enriched with the entering gas.

The rich oil is then passed to vent-abwrber I01, which is at a lower pressure than absorber I00. Flashing occurs in tank I01, the flashed vapors passing through partition III to the absorbing section of the vent-absorber, the oil passing on to the next two vent-absorbers I08, I00 which are at successively lower pressures than I01 and where the same action is repeated.

paratus and method. In this figure an absorber The unabsorbed flashed vapors after passing through the absorber section of tank I01 are oil is withdrawn through pipe H1 and pumped into the top of the absorbing section of tank I00,

from the lower end of which absorbing section it is pumped into the top of I01. The absorbing action 0! the oil is maintained in Ill and I" by the increased pressure in each case. The rich oil leaving I! is sent to the distillation unit through pipe "I. The foregoing steps demethanize the rich oil from absorber I00 while recovering the higher boiling constituents from the flashed vapors.

After demethanization the rich oil that has been venting in the vent-absorbers I01, I08 and I09 is passed through pipe H8 to a vent tank l2l, which may be, if desirable, operating at vacuum. The vapors here evolved are product. The oil leaving the vent tank is divided into two streams I28 and I29, one being the flash-vented oil that goes to the first absorber and the other going to the distillation unit where it is denuded by heat distillation. This lean oil then goes tothe top of the first absorber through pipe I and to the vent-absorber operating at lowest pressure through pipe 5.

' In the systems of Figs. 2 and 3 the heater or stripping may be used instead of pressure venting, or any combination of these methods may be used as in the system of Fig. 1.

This absorption system has all of the advantages of the others already described, and in addition it overcomes an objection in other systems combining flash-flood absorption and the conventional distillation method. The fault lies in the fact that while absorption in the first absorber depends on the degree of denuding of the flash-vented oil, vented components of the oil flashing in vent tanks are replaced when the oil from the reabsorbers is allowed to join the venting oil. As a result not only are some of the flashed hydrocarbons returned, but more absorption oil is added. This all tends to decrease the amount of vapor evolved in the final vent tank and causes a less denuded oil to be recycled to the first absorber. Since the absorbing oil in the vent-absorbers is kept separate from the venting oil in the instant system, the denuding of oil by flashing in the final vent tank is a maximum.

The amount of lean oil entering the ventabsorber operating at lowest pressure, namely I09, will be ample for the other absorbers since the largest volume of gas is evolved in that ventabsorber and furthermore its solvent power is maintained by increasing the pressure on it in each vent-absorber. The vapors leaving the vent-absorbers are sent to the next vent-absorber so there will be no loss of heavier constituents. Although the vent tank and reabsorber arrangement here described is applied where the vent tank and reabsorber are in one piece of equipment, it may be applied where vent tank and reabsorber are two separate and distinct pieces of apparatus.

We .claim:

1. The process of treating hydrocarbon gas comprising passing a stream of said gas in countercurrent relation to a stream of denuded absorption liquid in an absorption zone having initial and final points of contact between said gas and said absorption liquid, passing liquid eiliuent of said absorption zone to an ebullition zone, condens'ing resulting vaporous eflluent from said ebullition zone to form a high vapor pressure product, passing liquid eiiluent from said ebullition zone to a distillation zone, condensing the vaporous eflluent from said distillation zone to form a low vapor pressure product and recycling a controlled mixture of said products to said absorption zone at a point intermediate of said initial and final points.

2. The process of treatinghydrocarbon gas comprising passing a stream of said gas in'countercurrent relation to a stream of denuded absorption liquid in an absorption zone having initial and final points of contact 01 said streams relative'to gas flow, passing liquid eiiluent of said absorption zone to a second zone wherein ebullition of said eflluent takes place, passing liquid eflluent of said second zone toa third zone wherein ebullition of said emuent of said second zone takes place, recycling liquid eiiluent of said second zone to said absorber at an intermediate point in relation to said initial and final points, and recycling liquid eflluent of said third zone to said absorber at a point between said intermediate point and said final point.

3. The process of treating hydrocarbon gas comprising passing a stream oi. saidgas in c0un-.

liquid eiiiuent of a second ebullition zone having 7 a higher temperature than said first ebullition zone, to said. absorption zone at a point between said intermediate point and said final point.

4. The process of treating hydrocarbon gas comprising contacting a stream of the gas with a first stream of absorption liquid in an absorption zone having initial and final points relative to gas fiow whereby the absorption liquid be-t comes enriched with the gas, introducing a secand stream of absorption liquid to said absorption zone intermediate the initial and final points to join the first stream of absorption liquid, withdrawing the combined streams of enriched absorption liquid from the absorption zone at the initial point, passing enriched absorption liquid through a plurality of ebullition zones in succession. each succeeding ebullition zone having lower pressure than that preceding, recycling liquid eflluent from an ebullition zone to the absorption zone to form said second stream of absorption liquid, passing the vaporous eflluent of the first ebullition zone in contact with a third stream of absorption liquid to enrich the same, passing enriched absorption liquid to a distillation zone to denude the same, recycling denuded absorption liquid to the absorption zone at said final point to comprise said first stream of absorption liquid, and condensing vaporous effluent of the last ebullition zone and the distillation zone as product.

5. The process of treating hydrocarbon gas comprising contacting a stream of the gas with a first stream of absorption liquid in an absorption zone having initial and final points relative to gas flow whereby the absorption liquid becomes enriched with the gas, introducing a second stream of absorption liquid to said absorption zone intermediate the initial and final points to join the first stream of absorption liquid, withdrawing the combined streams of enriched'absorption liquid from the absorption zone at the initial point, passing enriched absorption oil from the absorption zone to an ebullition zoneyrecycling a portion of the liquid eflluent of the ebullition zone to the absorption zone to comprise said second stream of absorption liquid, denuda point between said intermediate point and said initial point.

6. The process of treating hydrocarbon gas comprising passing a stream of said gas in countercurrent relation to a streainof denuded absorption liquid in an absorption zone having initial and final points of contact of said streams aeeaaao relative to gas flow, introducing a stream of part to a still to denude the same. and passing the l denuded absorption liquid to the absorption zone as said stream of denuded absorption liquid.

7. The process of treating hydrocarbon gas comprising contacting the gas with an absorption liquid in a first absorption zone, passing the effluent of the, ilrst absorption zone through a plurality of ebullition zones in series, passing the vaporous emuent of each ebullition zone to sep arate reabsorption zones and passing a second absorption liquid through the reabsorption zones in series but in the opposite direction from that of the liquid eflluent through the ebullition zones.

8. The process of treating hydrocarbon gas comprising contacting the gas with an absorption liquid in a first absorption zone, passing the effluent ;of the first absorption zone through a pluralit'yof ebullition zones in series, passing the vaporous efliuent of each ebullition zone to separate reabsorption zones-passing a second absorption liquid through the reabsorption .zones in series but in the opposite direction from thatof the liquid efliuent through the ebullition zones,

and passing thevaporous ellluent of each reab- 

